The present invention relates to a method for the recovery of gold value from an aqueous solution. More particularly, the invention relates to a method for the recovery of gold value from an aqueous solution by using a specific solid ion-exchange adsorbent which efficiently adsorbs the gold value contained in an aqueous solution in the form of complex anions of gold even when the concentration thereof is very low.
It may be too much to say that, in addition to the traditional uses as ornamental or decorative articles, gold is widely used in various industries as a wiring material of electronic circuits in electronic industries or as a catalytically active ingredient in certain catalysts in chemical industries so that the demand for gold is rapidly increasing year by year. In view of the geologically very limited occurrence of gold as a natural resource, accordingly, it is or will be an indispensable technology to recover the gold value from various industrial waste materials. In particular, it is sometimes the case that the content of gold in certain waste materials coming out of the electronic industries is higher than the content in gold-containing ores occurring in nature so that it is an urgent problem under social needs to establish a technology for the recovery of the gold value from such waste materials. The aqueous wastes discharged from refineries of gold or depleted electrolyte solutions discharged from gold-plating plants always contain gold value but they are mostly discarded as such because of the extremely low content of gold therein requiring a great cost for the recovery of the gold value. It is eagerly desired therefore to develop and establish an efficient method for the recovery of the gold value contained in such aqueous wastes in an extremely low concentration from the standpoint of material recycling for the reservation of resorces.
As is well known, metallic gold can be dissolved in aqua regia to form an aqueous solution mainly in the form of chloro complex anions of gold while the aqueous wastes discharged from gold-plating plants using the cyanide-based electrolytic plating bath contain the gold value in the form of cyano complex anions of gold. Conventional processes for the recovery of the complex gold ions in such an aqueous solution include the methods of solvent extraction and ion exchange. The former method of solvent extraction using an organic solvent, however, is not always suitable for the recovery of the gold value when the concentration thereof in the waste aqueous solution is extremely low. The latter method of ion exchange using an ion exchange resin has a difficulty in respect of regeneration of the ion exchange resin. In order to solve these problems, Japanese Patent Publication 62-61535 and Japanese Patent Kokai 62-275024 propose a method for the recovery of complex anions of gold in a very low concentration by using a solid ion exchange adsorbent prepared by the adsorption of a high-molecular amine such as trioctyl amine on a porous polymer of a methacrylic acid ester or a quaternary ammonium salt such as methyl trioctyl ammonium chloride on a porous resin of an acrylic polymer as a resinous carrier. Although these carrier-supported solid ion exchange adsorbents can adsorb the complex gold anions, the lower limit of the concentration of the gold ions in an aqueous solution, from which the complex gold ions can be efficiently adsorbed on the adsorbent, is about 0.1 ppm by weight so that the method is not suitable for the recovery of the gold value from the wastes coming from the last stage of the refining process of gold or the aqueous wastes coming out of a gold-plating process in which the concentration of the gold value is sometimes so low as in the order of ppb by weight.